Biology Unit 6
Terms
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- How does meiosis result in genetic variability?
- During prophase I, the homologous pairs are very close to each other, thus they can switch end parts making the two chromosomes look different rather than identical as seen in mitosis and they are many different chromosome combos
- interphase I
- the chromosomes are replicated
- Prophase I
- eacb chromosome pairs with its corresponding homologous chromosome to form a tetrad. also, crossing over occurs which is when alleles are exchanged between homologous pairs.
- metaphase I
- homologous pairs line of in the middle of the cell
- anaphase I
- spindle fibers separate the homologous pairs of chromosomes to opposite sides of the cell.
- telophase I
- the nucleur membrane starts to reform. the homologus pairs are now in 2 different cells.
- Metaphase II
- sister chromatids line up in the middle of the cell
- anaphase II
- spindle fibers separate the sister chromatids to opposite sides of the cell
- telophase II
- final gametes are produces. there are 4 haploid cells each with half the amount of chromosomes as the cell began with.
- homologous pair
- chromosomes that are compatible because they carry genes for the same traits but one chromosome comes from mom, one from dad. 23+23=46 they look like X and are held together by a centromere
- purpose of mitosis/meiosis
- mitosis: division that results in growth and development, repair/asexual reproduction of body cells meiosis:division that results in gametes (sex cells)
- number of resulting cells in mitosis/meiosis
- mit-2 mei-4
- chromosome value of resulting cell in mit/mei
- mit-2N mei-n
- genetic info result in mit/mei
- mit-all identical mei-all different and varied
- where does mit/mei occur?
- mit-nucleus mei-reproductive organs-ovaries/testesorgans
- diploid cell
- A cell containing 23 pairs of chromosomes (2n), and each set contains a chromosome from mom and dad the total number of chromosomes is 46
- haploid cell
- A cell containing only one set of 23 chromosomes (n). only 23.
- Meiosis overview
- division when a diploid cell (46 chromosomes) is divided twice, once creating two diploid cells and a second time creating 4 haploid cells. it is necessary to have haploid cells because when an egg meets a sperm, then they will both have 23 chromosomes adding up to 46.
- 2 reasons meiosis is so important
- 1) it is a reduction division reducing the chromosome number in the gametes from 46 to 23. (cuts in half) 2) increases genetic variation in the offspring as no two gametes are the same
- sister chromatids
- Replicated forms of a chromosome joined together by the centromere and eventually separated during mitosis or meiosis II. (identical until crossing-over)
- overview of meiosis I
- the homologous pairs separate
- overview of meiosis II
- sister chromatids separate creating 4 haploid cells
- gene
- sequence of DNA that codes for a protein and thus determines a trait
- trait
- a characteristic that an organism can pass on to its offspring through its genes.
- dominant allele
- a genotype that is uncertain-there could be a dominant and dominant, or dominant and recessive.This allele will show up in an organism if it is present. it is marked by a capital letter
- recessive allele
- a genotype that is certain-there are recessive alleles from both parents and they both must be present to show up in an organism. They are marked by 2 lower case letters. it is hidden whenever the dominant is present.
- genotype
- letters to describe one's genetic make-up. (T, T)
- phenotype
- physical characteristics. ex-can roll tongue, hitchhiker thumb, etc.
- homozygous dominant
- one who inherits the genotype with 2 DOMINANT alleles. the genotype is TT or RR, etc. homo=same
- homozygous recessive
- when the alleles inherited are BOTH recessive (2 lower case letters) this is the ONLY time a recessive trait will appear. homo=same
- heterozygous
- term used to refer to an organism that has two different alleles for the same trait. one is capital, one is lowercase. the dominant trait will show because it will mask the recessive allele.
- How can you determine the phenotype of a person if given the genotype and vice versa?
- If given the phenotype, (ex-can roll tongue) you have to first find out which is the dominant trait, tongue rolling or not. Then, if you have a dominant trait, then the genotype will either be Rr or RR and if it's recessive, then it will be rr. If you have the genotype, ex-RR then you know it will be a dominant trait and you match that up with the trait you are looking at -ex-can tongue roll.
- monohybrid cross
- use a punnett square to look at the probability of inheriting ONE trait. includes complete dominance and incomplete dominance
- incomplete dominance
- neither allele for the trait masks the other. the heterozygous phenotype (one with R r) is somewhere between the two homozygous phenotypes. it is a mixture of the two. ex-RR-red, rr-white, Rr=pink!
- complete dominance
- when present, the dominant allele is always expressed and masks the recessive. the recessive is only expressed when a dominant is not present. (simple traits, tongue roll, etc)
- multiple alleles
- traits are controlled by a single gene, there are more than two alleles for the trait but an individual can only possess two alleles (one mom, one dad). ex-blood-there are two alleles dominant not over each other, but of one other type. blood-A and B will mask over O blood.
- autosomes
- chromosomes having to do with the chromosomes in the body. there are 22 sets of autosomal chromosomes.
- sex chromosomes
- chromosomes having to do with the X and Y chromosomes. A person only has one pair. if girl, XX. if boy XY.
- Karyotype
- pictures of every one of an organism's chromosomes. The sets are arranged from largest to smallest in their pairs. It can tell you if a person has the right amount of DNA, the sex (if XX or XY) and if there are large mutations.
- nondisjunction
- the failure of chromosomes to separate properly during meiosis (anaphase 1 and 2)
- monosomy
- a nondisjunction in which a member of a chromosomal pair is missing. Ex-2 in a pair, but only one is there.
- trisomy
- a nondisjunction in which a chromosome set contains 3 copies instead of 2 of a chromosome. this is because in meiosis, the homologous pairs or sister chromatids did not separate correctly.
- Nondisjunction in anaphase 1
- a normal division would have homologous pairs separate with one part of the pair on one side and the other part on the opposite side (dividing evenly) in a nondisjunction, an example could be if there were two sets of homologous pairs, and they separated so that one pair was still on the same side.
- nondisjunction in anaphase 2
- the homologous pairs separate normally, but then during the second round of division, instead of having two sister chromatids in each haploid cell, there might be three in one and only one in another.
- Mendel's law of independent assortment
- alleles for different traits segregate independently. ex- when alleles form into gametes, and if there is more than one trait in that gamete, one does not effect the other.
- Mendel's law of segregation
- Alleles segregate in the formation of gametes. one allele is from the mother and one is from the father and they combine into the same gamete.
- sex-linked traits
- When we use X and Y in our punnett squares. The trait is only carried on the X chromosome. Males are more likely to show these recessive disorders because they only have one X chromosome and cannot mask a recessive allele.
- pedigrees for autosomal traits
- 1) genotypes are "normal" (no X or Y) 2) individuals are either shaded or unshaded. not half 3)traits are expressed equally in men and women. the sex doesn't matter.
- pedigrees for sex-linked traits
- 1)genotypes have X and Y's 2) Females can be carriers. If heterozygous, then half shaded in. 3) men more frequently express the trait because nothing can mask.